p-Benzyne

Area of Science:

• Organic Chemistry
• Photochemistry
• Spectroscopy

Background:

• Diacetyl terephthaloyl diperoxide and dipropionyl terephthaloyl diperoxide are organic compounds.
• 1,4-diiodobenzene is an organohalogen compound.
• Low-temperature noble gas matrices are used to study reactive intermediates.

Purpose of the Study:

• To investigate the photochemical behavior of diacetyl terephthaloyl diperoxide, dipropionyl terephthaloyl diperoxide, and 1,4-diiodobenzene.
• To identify reaction products using infrared (IR) spectroscopy and computational methods.
• To confirm the formation of p-benzyne via pyrolysis experiments.

Main Methods:

• Photolysis of peroxides and 1,4-diiodobenzene in a low-temperature noble gas matrix.
• Infrared (IR) spectroscopy to detect reaction products.
• B3LYP computational calculations to predict IR absorption bands.
• Vapor-phase pyrolysis experiments.

Main Results:

• Photoreactions produced a compound with characteristic IR absorption bands at 725 and 980 cm⁻¹.
• These IR bands disappeared upon annealing the matrix.
• The observed IR bands matched calculated frequencies for 1,4-didehydrobenzene (p-benzyne).
• Vapor-phase pyrolysis of peroxides yielded a compound, (Z)-2, in high yield, confirming p-benzyne formation.

Conclusions:

• The photochemical decomposition of the studied peroxides and 1,4-diiodobenzene in noble gas matrices generates p-benzyne.
• IR spectroscopy combined with computational analysis is effective for identifying transient species like p-benzyne.
• Pyrolysis provides a complementary method to confirm the formation of reactive intermediates from peroxide precursors.